This invention relates to nuclear reactors and, more particularly, to the reactivity control of fission reactors.
Conventional nuclear fission reactors are controlled by control rods which are mechanically moved within the reactor core to control reactivity by changing the amount of neutron absorbing material in the reactor fission volume. The control rods can introduce a sufficient decrease in reactivity to control the reactor during positive reactivity transients arising from changing operating conditions. A reactivity control swing of only about 1% is typically adequate to provide control wherein the reactor can be reduced to a subcritical reactivity condition following a reactivity excursion. In routine reactor operations, an emergency insertion of the control rods is sometimes required to prevent an uncontrolled reactivity excursion.
It will be appreciated, however, that mechanical control rods have inherent limitations on the rate at which a negative reactivity can be inserted. Physical characteristics, such as inertia and rod length, limit the speed at which the control rod can be inserted into the reactor core. Further, the mechanical instability of the fuel elements in which the control rods are inserted can act to limit the insertion rate or even to preclude rod insertion.
These and other problems of the prior art are overcome by the present invention, and an improved reactivity control system is provided which is not dependent on mechanical components.
Accordingly, it is an object of the present invention to provide a control system for a nuclear reactor which does not depend on mechanical control rods.
It is another object of the present invention to provide a nuclear reactor control system which can introduce a negative reactivity at a very high rate.
One other object of the present invention is to provide a nuclear reactor control system which is inherently fail-safe.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.